The present invention relates to a method of priority assignment in a time-division multiplex communication (TDM) system comprising a loop to which a plurality of terminals of different priority classes and at least one supervisory unit are attached.
In TDM loop communication systems a channel which is represented by a frame (i.e. time interval) cyclically passing on the loop can be assigned to a terminal by the loop control unit, e.g. after a polling of all terminals over the loop or over separate service and control lines. In a simpler loop system requiring less central control, channels can be seized by the terminals without assignment. This requires only the provision of a special indicator in each frame which is changed from "free" to "busy" when a terminal occupies the channel.
Within the loop system, terminals of various speeds and of different importance are attached to the same loop. This type of system requires the introduction of a priority schedule so that when simultaneous service requests occur, certain terminals are serviced prior to others having a lower priority. A loop system with centralized assignment of channels may be adapted to handle such a priority scheme at the cost of additional storage or other hardware. The simpler system providing self-occupation of channels would, however, become much more complicated by such additional means for centralized priority handling.